1. Field of the Invention
The present invention relates to a device for hardening a foundry core from a mass containing sand in which the mass for hardening in the core form-tool is exposed to a gas stream enriched by a catalyst and, if necessary, subsequently to a compressed-air stream, with a mixing stage connectable ahead of the core form-tool for generating a catalyst vapor-carrier gas mixture which is in a flow connection with a catalyst receiver tank as well as with a program-controlled compressed-air source, by way of program-controlled valve means, pump means and flow meters.
2. Description of the Related Art
Such devices are well known; they allow for example, the so-called cold box casting process in which two components of an artificial resin system are added to the core sand which subsequently harden together with the sand as soon as an amine, for example an alkyl amine or a methyl formate, is added as a catalyst. In this, one component could, for example, be a polyester resin, a polyether or any artificial resin of liquid consistency with reactive hydroxyl groups; the second component is in every case an organic isocyanate. The two components are thoroughly mixed with the molding sand and then formed. Various attempts have been made to then catalyze the reaction and to render handling and use, in particular of the amines reliable.
Thus it has been well known for quite some time to push a mixture of tertiary alkyl amine and air through the isocyanate resin-sand mixture whereby this amine-air mixture is heated to a temperature of 30-50.degree. C. in order to vaporize all amine droplets.
However, the known processes have the common disadvantage in that the hardening process takes a considerable time. For example, mold release of the core-sand mixture in the form-tool often takes only a fraction of a second on a core shooter; by contrast, subsequent gasification for hardening the core needs to be maintained for several seconds. Naturally, as a result, gasification is enormously costly.
In order to reduce gasification time or hardening time, as a rule, it became customary to add an overdose of amines, with the danger of renewed liquification of the binders occurring thus reducing the possible final strength of the core to approx. 80 to 85%.
Later, a further process became known in which dispenser pumps are to be used between the catalyst source and the mixing station for carrier gas and catalyst, in order to be able to dispense the catalyst better. However, here too, this can only bring about an unsatisfactory result because the pressure conditions in the first runnings of the catalyst are at first absolutely indifferent with each dispensing action.
Subsequently, somewhat better results were achieved in that both the catalyst vapor-carrier gas mixture and the compressed air are each stored temporarily in a dispensing container, and from these dispensing containers they are then shot into a core, in sudden consecutive blasts, whereby the compressed air is stored with a larger volume and heated to a higher temperature than is the case with the catalyst vapor-carrier gas mixture.
However, technical expenditure for these measures is enormous and plants of this kind allow few variables.
It has therefore been proposed that for the production of the catalyst vapor-carrier gas mixture the catalyst be added in liquid form to a jet ahead of the heating stage, whereby its exit jet, influenced by an additional atomizing gas streaming through the jet, disintegrates.
However, such equipment allows only gasification with very inaccurate dispensing.
It is thus the object of the present invention to create a device of the type mentioned above which allows the most optimal dispensing of the required catalyst with the shortest gasification time, and at the same time the use of the most varied processes with the most varied parameters, such as subsequent pressure stages or proportional pressure increase, different quantities of catalyst gas and time discretion for the charging of carrier gas or compressed air.